The present invention relates to novel polymeric molding compositions comprising an amorphous polymer matrix and an inorganic filler. More particularly the present invention relates to such a polymeric blend having improved properties, particularly reduced coefficient of linear thermal expansion (CLTE), a high dart impact resistance, and good resistance to the effects of heat. The above composition is particularly useful in the preparation of molded objects particularly parts having large surfaces prepared by injection molding techniques and having predictable finished dimensions and smooth finish. Such properties are particularly desired for exterior automotive body panels.
U.S. Pat. No. 4,098,734 discloses blends comprising a matrix interpolymer, a grafted rubber copolymer, a polymer other than the two foregoing polymers having a solubility parameter in the range of 8.5 to 13 and an inorganic filler. Examples of such blends comprising an ABS resin, about 14 percent of a clay, and polymethylmethacrylate or cellulose butyrate were disclosed. The reference further taught that polycarbonate could also be employed in the blend.
In JP 52 63,954 there are disclosed blends composed of 20 to 45 weight percent of an ABS resin, 45 to 20 weight percent of a polycarbonate resin and from 5 to 30 weight percent talo. Such compositions have been found to lack suitable heat distortion properties and also to be deficient in toughness as measured for example by Dart impact resistance or notched Izod impact values.
In certain applications such as exterior automotive injection molded parts it is desirable to provide low temperature impact resistance as well as reduced coefficient of linear thermal expansion and high temperature distortion resistance all in one polymeric resin. Unless the coefficient of linear thermal expansion (as measured according to ASTM D696) is less than 3.9.times.10.sup.-5 /.degree. F. over the temperature range of 70.degree. to 120.degree. F. extremes in temperature conditions can result in misfitting of various components of the finished assembly. A door or fender component which expand excessively will in extreme heat conditions result in buckling or misfit in the assembled finished product. Equally important is impact resistance as measured by dart impact resistance, particularly at low temperatures when thermoplastic resins are particularly subject to cracking under impact. Generally improved coefficients of linear thermal expansion can be obtained by the incorporation of increased amount of fillers, however, impact resistance, particularly low temperature impact resistance, is often reduced to unacceptable levels. Fibrous reinforcing additives such as fiber glass are very efficient in lowering the CLTE, however, such fibers typically are visible in the surface of the resulting object thereby producing unacceptable surface properties.
Accordingly it would be desirable if there were provided an improved polymeric blend having both a reduced coefficient of linear thermal expansion while retaining acceptably high dart impact resistance, particularly low temperature dart impact resistance.
In addition it would be desirable if there were provided such an improved polymeric blend that additionally retains a high heat distortion under load such that parts prepared therefrom may be exposed to elevated temperatures without distortion.